A Comprehensive Introduction To Float Glass Furnace: Port and Regenerator

Port and regenerator are the main parts of a glass furnace. There are two combining forms for the port and regenerator, box-shaped and half-box-shaped. Furnaces fueled with oil and natural gas adopt the box-shaped combination. Furnaces fueled with producer gas adopt half-box-shaped combination. The port and regenerator of float glass furnaces are respectively set on the two sides of the furnaces and arranged symmetrically. Based on the melting capacity, 4-10 pairs of ports are set.

(1) Port

According to the fuel used, different types of float glass furnaces are used. For furnaces fueled with producer gas, its combustion device is called port. For furnaces fueled with heavy oil or other liquid fuels, its combustion device is called nozzle.

The port is an important part of glass furnaces where fuel and air are preheated and mixed and where combustion is performed. It can ensure the length, brightness, rigidity, and sufficient coverage of flame and make the flame not flighty and not hierarchical and meet the temperature and atmosphere requirements.

Coal gas and air are preheated in the regenerator and then respectively into the pre-combustion chamber through the vertical channel (rising road) and a horizontal channel. They are mixed in the pre-combustion chamber and partially burned. Then the mixture is sprayed into the furnace a certain direction and velocity and continues to burn. The flue gas goes across the opposite port. Thus, the port acts as an air passage and the exhaust passage. But, the structure of the port is important for the heat transfer and glass melting.

Currently, float glass furnaces with a melting capacity of more than 400 t/d are equipped with 6 pairs of ports and 700 t/d + furnaces 7 pairs of ports, or even 10. When designed the port, the properties of oil, coal and gas determines the technical parameters of the ports, say, the ratio of the total area of the port mouth and the area of the melting zone, the declination angle of the skew arch of port, etc..

The port consists of the top arch, sidewall and bottom. The arch connecting the port and the melting furnace is called the jack arch of port. The arch connecting the port and the regenerator is called the back jack arch. the middle arch is called the skew arch of port. The arch, sidewall and bottom form the port space. The jack arch of float glass furnaces always adopts the plug-in structure, with flat top surface and arcuate bottom surface and matches with the breast wall of the melting furnace. since the breast wall is interward tilted intentionally and the crown and crown edge bricks are directly pressed on the breast wall, the jack arch of port should adopt the same structure. This structure is currently widely used.

The skew arch is an important part of the port and its structure should match with the structure of the jack arch. The back jack arch, sidewall and bottom are simple.

Besides the differences mentioned above, the main difference between the coal gas port and the oil port is the tongue of port. In general, the tongue is 400-450 mm. Generally the coal gas port is 400-500 mm height and the rise to span ratio is 1:10.

Currently there are two types of skew arch: the straight type and the flare type. The straight type is easy to mix fuel with air since the coal gas is platy when our of the rising channel. The mixed gas has little erosion on the sidewall of port. This structure is simple and easy to construct. The flare type can force the flame diffuse and spread and improve the coverage of the flame and the adverse maintenance situation caused by the narrow rising channel of coal gas.

(2) Regenerator

The regenerator is a waste heat recovery device, a part of the waste heat reuse system. It is built with refractory bricks known as checker bricks. It accumulates part of the heat in the exhaust fumes for heating air. When high temperature exhaust gas flows through the checker work, it heats the checker bricks. In this process, part of heat is stored in the bricks. Then when the flame turns, the heat stored in the bricks heats the coal gas or air that flows through the bricks. In this process, the bricks are cooled. This cycle is repeated. So, the regenerator is to transfer the heat in the exhaust gas to the air and coal gas through checker bricks. It can save fuel and reduce cost.

The exhaust gas discharged from the furnace is around 1400-1500℃, which can preheat the coal gas to 800-1000℃ and the air to 1000-1200℃. The exhaust gas discharged from the regenerators is around 600℃.

The regenerator is composed of top arch, external and internal sidewalls, the end wall, partition walls, checker work and rider arch. The top arch is generally 350 mm thick or thicker, built with silica bricks, with a central angle is 90-120°. The sidewall, end wall and partition wall are generally 580 mm thick, built with low porosity fireclay bricks in the lower part and basic magnesia bricks in the middle or top part, sometimes silica refractories in the top part.

The connected structure has a connected air regenerator under one of the ports. The coal gas regenerator is also a connected chamber. Since the airflow is not even in the regenerator, it is easy to burn the checker bricks by local overheating. Now it is seldom used.

The partition structure has two separated chambers. Air in the two chambers can not circulate. The distribution of the gas in each chamber is adjusted with the dampers in the branch flues. It can adjust the gas distribution easily and hot repair the checker bricks conveniently, but since there are many partition walls, the area of the checker bricks and heat exchange area are reduced, so the thermal efficiency is not high.

In the semi-separated regenerator, the flues above rider arches are separated based on each port. The regenerator itself is not separated. The dampers for adjusting gas distribution are set on the branch flues.

In the two-port connected regenerator, every two ports are separated into a chamber, while a port has a branch flue to adjust the gas distribution of each port. Since there are less partition walls, the heat exchange area is increased, so the thermal efficiency is improved. But the deceasing of partition walls reduces the stability of the sidewalls. Besides, it makes the hot repair of the checker bricks difficult, since two connected ports must be repaired together, which can severely affect production. This structure is mainly used in large float glass furnaces.

In the two-segment regenerator, a regenerator are separated into two parts, a high temperature zone and a low temperature zone. The two parts are connected with a vertical channel. This structure can prevent the corrosion by the phase transformation of sodium sulfate to the checker bricks. but this structure is complex and seldom used now.

The completely connected regenerator is completely connected, while the gas distribution of each port is adjusted with branch flues. This structure can increase the heat exchange area of checker bricks and improve the thermal efficiency. Since there is no partition wall, the stabiltiy of the sidewalls is poor. If there are local collapsing or clogging of checker bricks, it will be difficult to hot repair. Currently, this structure is used in large float glass furnaces.

Rider arch is a refractory structure to support checker bricks. It is an arch structure, built with arch bricks. Joints are reserved between rider arches for ventilation. Since checker bricks are laid on it, its top surface should be made level. There are two methods for leveling. One is to make it level with bricks on the arch. The other is to make it level directly with arch bricks with flat top surface and arcuate bottom surface.

The width and height of rider arches are determined by the weight of the checker bricks it bears. Generally, its width is not less than 150 mm and its height is not less than 300 mm. The internal space should be not less than 150 mm.

Checker work is the heat transfer part of the regenerator, the most important part of the regenertor. Its structure affects the service life of the regenerator and the regenerative effectiveness, thereby affecting the thermal efficiency of the melting furnace. The refractory materials for checker bricks should have good high temperature resistance, corrosion resistance, high regenerative capacity, fast heat transfer and good thermal shock resistance as well as good structural stability.